1. Field of the Invention
Embodiments of the invention can be applied to special advantage but not exclusively in the field of medical imaging and medical diagnostic apparatuses. These diagnostic apparatuses are X-ray image acquisition apparatuses.
2. Description of the Prior Art
Today, X-ray apparatuses are used to obtain images, or even sequences of images, of an organ located in a living being, especially a human being. The X-ray apparatus has an X-ray tube generally contained in a metal sheath or casing. This metal sheath provides firstly electrical, thermal and mechanical protection for the X-ray tube. Secondly, it protects operators from electrical shocks and X-rays.
The X-ray apparatus has a high-voltage generator supplying the X-ray tube with energy. The generator is powered in certain cases by a power supply battery or power battery. When the high-voltage generator supplies the tube with a pulse of about 100 kilovolts, a sudden current draw on the power battery is generally observed. The power battery almost instantaneously reaches its peak value. This value then decreases in a substantially exponential way to swiftly reach its constant operating value. When the pulse given by the generator is terminated, the power battery suddenly stops powering the generator.
It is therefore important to reduce the peak value and the root-mean-square value of the current delivered by the power battery, in order to reduce the shocks received by the power battery. The current delivered by the power battery is very high, even for short high-voltage pulses given by the generator. This current also remains very high even when the mean power is reduced, i.e. with a duty cycle or duty cycle of ⅓. This duty cycle is the ratio between the duration of the pulse and the interval between the pulses. This duty cycle is used to compute the real time during which the pulse itself lasts.
The peak value and the root-mean-square value of the current of the power battery provide information on the life of the said battery. These power battery current values therefore lead to determining the power battery to be chosen to power the generator.
A classic solution exists to resolve the drawbacks caused by the very high rates of current of the power battery. In this classic solution, a bank of capacitors is parallel-connected to the supply battery. An example of this kind of solution is shown in FIG. 1.
FIG. 1 provides a schematic view of a topology of an X-ray apparatus 10 comprising means capable of reducing the current of the power battery. The X-ray apparatus 10 of FIG. 1 comprises a tube 11 powered by generator 12. This generator 12 delivers high-voltage pulses, for example 20-kilowatt pulses, to the tube 11. The generator 12 is powered by a power battery 13. To prevent current peaks in the power battery, a capacitor bank 14 is parallel-connected to the power battery. When energy is drawn from the generator 12, the capacitor bank 14 behaves like a discharge system and shorts the power battery 13.
The result obtained with this type of topology is shown in a graph of FIG. 2. In FIG. 2 two distinct curves are used to show the progress in time of the high voltage powering the tube and the power supply current powering the generator during a radiology examination.
The x-axis in FIG. 2 represents the time in milliseconds. The y-axis to the left represents the high voltage in kilovolts. The y-axis to the right represents the current in amperes given by the power battery. The curve 15 represents the progress in time of the high voltage powering the tube, during a radiology examination. The curve 16 represents the progress in time of the current delivered by the power battery during a radiology examination.
At the step 17, the high-voltage generator gives the tube a pulse of about a hundred kilovolts as shown by the curve 15. To this end, the power battery gives the generator a high-power current, as shown in the curve 16(Ibat).
This pulse given has a width of 10 milliseconds in the example of FIG. 2, and lasts up to the step 18. Between the steps 17 and 18, the tube converts the energy given by the generator into X-ray intensity.
The step 18 marks the end of the pulse given by the generator. From the step 18 to the step 19, the current of the power battery is gradually reduced as compared with the prior art where the current was stopped suddenly. As can be seen in the curve 16, the current delivered by the power battery is filtered by the capacitor bank. This prevents current peaks so that the battery has to withstand fewer shocks.
However, this type of classic solution is not optimal, for this type of circuit is solely passive.